US3185201A - Combustion device with thermoelectrically powered burner - Google Patents

Description

May 25, 1965 w. A. HERBST ETAL. 3,185,201

COMBUSTION DEVICE WITHTHERMOELECTRICALLY POWERED BURNER Filed July 6. 1961 2 Sheets-Sheet 1 STY A N ROBERT L. WEEKS JAMES A. WILSON PATENT ATTORNEY May 25, 1965 w. A. HERBST ETAL 3,185,201

COMBUSTION DEVICE WITH THERMOELECTRICALLY POWERED BURNER Filed July 6. 1961 2 Sheets-Sheet 2 ROBERT L. WEEKS JAMES A WILSON BY @LWB TM PATENT ATTORNEY United States Patent O 35,201 COMBUSTEON DEVICE WiTH THERMO- ELECTRICALLY PWERED BURNER Walter A. Herbst, Union, Robert lL. Weeks, Scotch Ilmns,

and James A. Wilson, Stanhope, NJ., assignors to Esso Research and Engineering Company, a corporation of Delaware Filed July 6, 1961, Ser. No. 122,268 4 Claims. (Cl. 15S- 4) This invention relates to a heating system which includes a combustion chamber, a thermoelectric generator associated with such chamber, and an electrically activated burner means including a transducer driven by an electronic oscillator powered by such generator. This invention relates particularly to an oil burning, home heating system comprising a combustion chamber, a thermoelectric generator including a plurality -of thermocouples each having one end intimately associated with such chamber and a hollow burner means designed to admit of passage of a fuel oil stream therethrough, positioned to direct such stream into said combustion chamber.

It has been suggested in the art to associate thermoelectric generators with the combustion chamber of a domestic heating plant and utilize the resulting power to activate pumping means associated with the fuel supply or an air impelling device. In systems of this type the power generated must be sufficient not only to transfer the liquid fuel to the combustion chamber but to provide also through pumping means a sufcient pressure for atomization of such fuel for effective burning. To meet these power requirements Without a marked increase in thermocouple productivity over the present state of that art the size of such generator and the number of producing elements therein can become excessive. In the instant invention highly eiiicient atomization is achieved by ultrasonic vibrational means activated by a low power input electronic driver.

In a preferred embodiment of this invention the ow of air or water, past the cold ends of the thermocouples, employed to provide the requisite temperature differential for power generation is effected countercurrent to the temperature gradient in the combustion chamber. This results in maximum eiciency of heat transfer.

In a preferred embodiment of this invention the heating apparatus is designed so as to partition into separate compartments a heat exchange space provided between an outer housing and an inner combustion chamber, said separate compartments being enclosed by a iirst conduit and a second conduit formed by said outer housing and the Wall of said combustion chamber. One of these compartments provides for circulation of a heat transfer material for space heating, e.g. air or water, another compartment provides a hot water supply within an independent circulatory system. With the temperature being different for the separate circulating media this invention is uniquely adapted to and is preferably carried out utilizing thermoelectric elements which reach their maximum eicency at different hot junction temperatures. In operation, one junction of a thermocouple is in Contact with a source of heat while the other is in thermal contact with a heat sink. Thus, the thermoelectric elements herein may be employed in two or more groups and spaced in relation to the temperature gradient along the combustion zone in accordance with their respective eiiiciencies at different temperature levels.

A semi-conductor is, as is well known, an electrical conductor with a iinite forbidden energy gap between its valence conduction bands. It is within the scope of ll Patented Mey 25, 1h65 this invention to employ as thermoelectric elements semiconductors classified by the art as either intrinsic or extrinsic, n-type or p-type. Furthermore, it is within the scope of this invention to employ thermocouples of any composition which will perform satisfactorily within the temperatures of operation existing at the part of the combustion chamber with which such couple is associated. The size, shape and fabrication of such thermocouples may be varied so as to adapt to the over-all design of the heating unit.

Among the suitable semi-metallic alloys that may be used for thermoelectric elements are combinations of indium and arsenic; indium and antimony; lead, selenium and/or tellurium, etc.

Metallic thermocouples, eg. combinations wherein one element is a chromium steel alloy and the other is Constantan (a nickel-copper alloy) or Copel, may also be used.

In this invention electrical energy from the thermoelectric generator associated with the combustion chamber provides power for an electronic oscillator. The latter serves as a driving means for a transducer apparatus which in turn is utilized to atomize fuel for eiiicient burning. The transducer, when associated with appropriate housing means and conduit means for receiving fuel, constitutes or is included in the burner device of the instant combination. The transducer employed comprises a piece of ceramic piezo-electric material such as barium titanate bonded to or held in close contact with a at surface to the larger diametral surface of a stepped cylinder or truncated, conical, etc., resonator of elastic and electrically conductive material such as aluminum.

When an alternating voltage of relatively high frequency is applied across the ceramic piece, this piece will be cyclically thickened and thinned and will generate alternate compression and rarefaction waves of sonic energy. This energy, which may be characterized by a frequency within or preferably above the range of normal hearing will cause a cyclical lengthening and shortening or longitudinal vibration of the metal resonator as it flows thereinto. With decreasing cross sectional area of the resonator in the direction away from the ceramic piece, there will be a concentration of energy near the resonator tip and an increasing amplitude of motion. When a drop of liquid such as heating oil is applied to the resonator tip while the resonator is being vibrated longitudinally, sonic energy will flow into this drop and the drop will be broken up into a fog of line particles, that is, it will be atomized.

Activation of the transducer so as to perform its intended function requires a driving means, that is, a means whereby and wherefrom alternating voltage is supplied to the transducer. The driving means employed herein comprises an electronic oscillator.

A sonic energy transducer of the kind described is, like many other components used in alternating current circuits, characterized by a figure of merit or efficiency coeiicient generally designated Q Q represents the ratio of energy stored in the component to the energy lost therein or therefrom during equal intervals of time of an operating cycle. For a transducer comprising a disc of barium titanate bonded to the base of a conical aluminum resonator the over-all or composite Q will often be as great as 2,500. This is a relatively high value, and signifies that the transducer has quite a sharp resonant peak; that is, its frequency of excitation by input voltages from the driving means must lie in a relatively very small range or narrow band for achievement of a substantially maximum amplitude of longitudinal vibration.

The electronic oscillator employed herein is designed to provide Class C operation with current feedback. The

,are sustained at a selected mechanical harmonic frequency of the transducer which is dictated by the tuned circuit. Also a safety circuit is included to control the supply of liquid to the transducer in such a way that there Will be a flow of liquid only when driving power is furnished to the transducer.

One object of this invention is to provide a highly eicient home heating system utilizing ul-trasonic vibrational atomization of an oil fuel activated by a low power input electronic driver and which does not require an outside source of electrical power.

Another object of this invention is lto provide an oil fired heating system wherein electrical energy produced therein by thermoelectric generation provides power for both fuel atomization and for recharging during operation the storage batteries employed for system startup.

Other and further objects of the invention will become apparent as the description proceeds, reference being had to the accompanying drawing illustrating one form of the invention wherein:

FIGURE l is a schematic side view in cross section of a fluid fuel burning apparatus having a thermoelectric generator incorporated therein and equipped with a burner designed to provide fuel atomization via generation of alternate compression and rarefaction waves of sonic energy.

FIGURE 2 represents a diagram ofthe electrical circuit suitable for use in effecting the combination of this invention including the thermoelectric generator and sonic energy transducer-burner of FIGURE 1 with an electronic oscillator interposed therebetween, such oscillator being powered by such generator and serving as the driving means for such transducer.

Referring now to FIGURE l, this is a schematic sideview in cross section of a combustion heating apparatus 1 which, in the embodiment shown here, includes a fuel feeder unit 2 and a heater unit 3. Heater unit 3 includes an outer housing 8, shown as cylindrical in form, although it can assume other shapes, enclosing a heating chamber or combustion chamber 9. Around part of chamber 9 is a first heat transfer chamber or compartment 10 for supplying heat to a space heater circulatory system. A second heat transfer chamber or compartment 11 surrounds a further part of chamber 9 for providing a hot water supply. As it hasV a decreasing temperature gradient from left to right, as seen in FIG. l, the combustion chamber may be considered to have successive temperature zones or subzones adjacent the respective heat exchange compartments 10 and 11. T-hat part of combustion zone or chamber 9 which is adjacent compartment or chamber 10 may be considered a first zone of high temperature range. That part which is adjacent compartment or chamber 11 may be considered v `a second or lower temperature zone. The outlet of chamber 9 is an exhaust conduit 12 through which combustion gases aredischarged from the apparatus. A thermoelectric generator or thermopile 13 is Ybuilt into the wall Y betweenV zone or chamber 9 and the air or water jacket zone 10 and water jacket zone 11. The thermoelectricV generator 13 includes a tubular member 14 formed of electrically insulating refractory material and which extends coaxially'with housing 8 so as to define combustionV chamber l9, a plurality of substantially radially extending thermocouples 15 connected in series or in both series Yandparallel by conductors not shown and having hot by tubular member 14whi`ch is a nonconductor.

In one embodiment the thermocouples are protected from direct contact with the combustion gases of chamber 9 by a combustion chamber liner, not shown. Appropriate material between such liner and the thermoelectric elements provides electrical insulation from the liner without appreciably reducing heat transfer. A similar liner, again appropriately insulated, may be disposed between the elements and the heat'transfer chambers 10 and 11. Electrical connection between'the appropriate portions of such elements may be effected by conductors in accordance withv conventional practice.

Thermocouples 1S in FlGURE l are divided into"high temperature thermocouples 15a which reach their maxi-Y mum eciency at relatively high temperatures, i.e. within the temperature range existing immediately -forward of burner 5, hereinafter described, e.g. from about 900 to 1700 F., and low temperature thermocouple's. 15b which reach their maximum eiiciency at temperatures of up -to about 700 F. below those of the aforesaid range. In other words, the high temperature thermocouples 15a are chosen so that they oper-ate at maximum eihciency within the first temperature range or zone and thermocouples 15b are chosen so that they reach Y their maximum efiiciency in the second temperature range or zone. YAs is known in the art, the thermoelectric elements are made up of materials known as semi-conductors. A p type and an n type must be in electrical contact to form one junction of the thermocouple. Suicient numbers of the couples `are arranged in series and/or parallel arrangements to provide the voltage and amperage necessary to the operation of the device. The so-called high temperature therrnocouples may consist of compositions of iridium and arsenic; compositions of lead, selenium and/ or tellurium which may also include dopings of sulfur, Bi, Ta, Mn, Zn, Ti, Al, Ga, etc. The high temperature thermocouples and the low temperature thermocouples may consist of the same materials with a different ratioY of the same components employed. While for purposes of simplification the thermocouples are shown to be divided into only two groups, it should be understood that more than two types of thermocouples, i.e. thermocouples of different design or composition, may be utilized in accordance with their eiiiciency ranges. Thus one might employ an iridium-arsenic combination above 900 F. followed by an iridium-antimony combination in the area immediately downstream Ifrom the burner where the operating ternperature range is about 600 to 900 F. and beyond this combinations such as Bi(Te, Se)3. This invention, however, does not reside in the shape or composition of the thermocouples employed and it is within the scope of this invention to use any of the various thermocouple designs and materials known to the art for thermoelectric generation of electrical energy at operating temperatures within the temperature ranges employed in conventional oil burner home heating systems. Conduit 19 provides inlet means for a heat transfer medium, e.g. air or water, to chamber 10 where such medium acquires heat generated in combustion zone 9 and leaves chamber 10 via conduit 20 for use in spacerheating.V Conduit 21 provides inlet means to chamber 11 for water to be heated in chamber 11 and passed on to hot water storage via conduit 22. As indicated by the arrows, theow of heat transfer medium in both chambers is preferably countercurrent to the temperature gradient, i.e., the cool uid enters the end remote from the burner and exits at the end nearest vthe burner. Wires 24, 25 and 26 represent electrical connections for/transfer of electrical energy Yan ultrasonic type burner nozzle or Vatomizer 5 having an outlet opening V5a. Fuel oil is admittedjto nozzle 5 by fuel conduit 6 via electrically controlled valve 7.. The construction and operation of nozzle 5 and valve 7 will be discussed in greater detail hereinafter in the description of FIGURE 2 andelsewhere in the specification. The outlet opening 5a of burner nozzle or atomizer 5 is disposed in substantially concentric alignment with opening 23 into combustion chamber 9. Housing 4 is here shown mounted on housing 8 and positioned to circumscribe opening 23 and nozzle 5 which is supported in place by support means positioned in the cutaway portion of housing 4, not shown here. Combustion air is admitted to combustion chamber 9 through opening 23 around nozzle 5 from an air impelling device, e.g. an electrically driven fan or blower 41. Fuel oil may be provided to nozzle 5 by either a gravity feed or pumping means.

Referring now to FIGURE 2 in detail, 13 represents thermoelectric elements mounted so as to be energized by heat generated by burning fuel as portrayed in FIGURE l. They are of different composition so selected as to provide maximum eliiciency for the temperature range of operation. Conductors 24 and 25 are terminals by means of which the total electrical output from all the thermoelectric elements are made available for the operation of the burner operating circuit. These elements are connected in series with battery terminals T3 and T4 through switches S1 and S2 operated by relay Reon signal from the thermostat on-oif control S3 so that during the Warmup period power for the operation of the device, power for the transducer or atomizer nozzle can be provided by storage batteries B1 and B2. (In lieu of batteries, suitable transformers of low frequency A C. house current may be used.) This arrangement has the added advantage that after the device has reached operating temperature, power from the thermoelectric elements will be available for recharging the batteries, eliminating the need for recharging B1 and B2 from time to time by an outside electrical source. On starting up, the thermostat S3 causes S1 and S2 to close. After the thermal generator starts up, the batteries are recharged. A suitable voltage regulator, not shown, will be provided in the battery circuit to prevent overcharging.

Conductor 26 is a terminal connected to an intermediate point in the thermoelectric element arrangement. Iust suhcient voltage is generated across 24 and 26 to provide the necessary power for heating the filament in a vacuum tube V1, i.e., about 150 milliamperes. A connection is made with battery B2 through terminals T6 and T4 to provide the necessary lament current during the warmup period. C1A and C1B are 4type M-l50 silicon diode rectiiiers. They provide a one-way path for the ow of electrical power from the thermal element to the oscillator circuit and batteries. They prevent the discharge of the batteries when the thermal is less than the battery L1 is a 30-millihenry, 20-ohm DC. inductor which affords a low resistance direct current path between the power supply and the plate of vacuum tube V1. Conversely, it provides a high resistance path for high frequency alternating current, that is, for currents having a frequency on the order of 50 kilocycles/sec. and higher.

Vacuum tube V1 is a type 50L6 beam power tetrode having a SO-volt filament. C2 is a 0.1 microfarad capacitor which prohibits direct voltage on the plate of vacuum tube V1 from reaching the terminals of sonic energy transducer or burner nozzle 5. On the other hand, this capacitor acts as a coupler affording a low resistance path for the flow of high freqency alternating current to the transducer terminals from the plate side of the tube. C3 is a 0.005 microfarad capacitor which acts as a block to prevent direct current short circuiting to ground of the control grid of vacuum tube V1 through grid tuning coil L2, but affords a low resistance path for the flow of high frequency alternating current from coil L2 to the control grid.

R1 is a 47-kilohm resistor which provides a path for the iiow of direct current induced in the control grid circuit by the presence of high frequency alternating current at the grid terminal. This resistor develops a control grid bias for vacuum tube V1. C4 is a 0.1 microfarad capacitor which isolates the power supply from the frame ground of the equipment, but acts as a coupler to provide a low resistance path for the ow of high frequency alternating current to the terminals of sonic energy transducer or nozzle 5. C5 is a 33-micromicrofarad capacitor which permits negative feedback from the output circuit to the contro-l grid of the vacuum tube. Negative feedback from output to input of a circuit generally has the effect of reducing output. It is employed in the oscillator circuit of this invention to effect an improvement in power factor, specifically, to improve the phase relation of voltage and current to transducer 5.

L2 is a l0-millihenry grid tuning coil having a Q of at least 100. C6 is a grid tuning capacitor having a range up to 1000 micromicrofarads. The combination of inductance and capacitance provided by L2 and C3 is tuned to the mechanical harmonic frequency at which transducer 5 is to operate, a frequency of 70,000 kilocycles/ sec. for example. L3 is a 0.6 microhenry current feedback coil having many times fewer turns than grid tuning coil L2. Coils L2 and L3 are, however, electromagnetically coupled closely together. The output current from vacuum tube V1 to transducer 5 liows through coil L3, inducing a voltage in coil L2 which appears at the control grid of the tube. The voltage so appearing represents positive feedback, and causes the circuit to sustain itself in an oscillating condition. This feedback and oscillationsustaining effect occurs most eciently when grid tuning coil L2 and capacitor C6 together are tuned to an active mechanical harmnoic frequency of transducer 5.

Transducer 5, as shown, comprises a relatively thin disc of piezo-electric material P-1 bonded to the larger end of a metallic and electrically conductive resonator RSwl, shown here, as of truncated conical form. This transducer, the illustrated design of which is representative only, is characterized by an axial hole 5a through both elements Pel and RS-l. Fastened to piezo-electric element P-l in alignment with this hole is a liquid feed conduit 6 which includes a solenoid-operated stop valve 7. In the absence of energizing current to its coil element, valve 7 is normally closed.

, C7 is a 10G-microfarad capacitor, and R2 is a lO-kilohm resistor. High frequency alternating voltage from vacuum tube V1 appears across capacitor C7 and resistor R2 in series. Capacitor C7 serves to block the ow of direct current from the plate of vacuum tube V1. A reasonable amount of high frequency alternating current will be passed by capacitor C7 acting as a coupler between the oscillator circuit itself and the safety circuit including relay Re-Z which serves to prevent flow of liquid for atomization to transducer 5 except when the transducer has driving power furnished to it.

Resistor R2 acts a a proportioning device in respect of alternating current passed by capacitor C7 to allow enough current to be supplied to rectifier C3 to satisfy the operating requirement of relay Re-Z, about Z2 milliamperes direct current, which is normally open across its external terminals T7 and T3. Rectifier C8 is a type IN34 germanium device which receives alternating current from vacuum tube V1, and passes a pulsating direct current. C9 is a 0.1 microfarad capacitor which acts as a storage device for this pulsating current which ows through the coil element of relay Re-Z and also through resistor R2. When there is an adequate amount of high frequency alternating current available from the oscillator circuit at capacitor C7, relay Re-2 will be energized to close across terminals T7 and T3. Upon the effecting of closure across these terminals a power circuit will be completed through the coil element of solenoid-operated valve 7 to open this valve, and allow liquid for atomization to iiow through conduit 6 into transducer 5.

The oscillator as described affords a means of obtaining relatively large plate currents at low plate voltages in 7 vacuum tube V1. This provides efficient coupling for transducers such as sonic energy transducer 5 having load resistances in the rangeV of about 100 to 1000 ohms. The basic control of oscillation is exerted through the transducer, and changes in the resonant frequency of the transducer due to changes in temperature, for example, result in corresdonding changes in the operating frequency of the oscillator.

The resonant frequency of operation of sonic energy transducer 5 is a series resonant frequency. Accordingly, v

maximum transducer activity or performance is obtained at a condition of maximum current. Transducer current flows through feedback coil L3 coupled to tuning coil L2 of the grid circuit to provide positive feedback, and therefore the higher the transducer or output current, the higher the control grid voltage of tube V1. Grid bias on the vacuum tube of the oscillator of this invention is sustained at an average level about double the amount required to cause plate current to cease to ilow.

A -transducer intended to be driven by the oscillator of this invention'may have more than one resonant frequency; that is, longitudinal vibrations may be sustained in it at more than one mechanical harmonic or mode designated as half wavelength, full wavelength, three halves wavelength, etc. It is desirable to select the one of these harmonics for the oscillator/driver operating point which will be the most eiiicient with respect to energy conversion in the transducer. The tuned circuit including coil L2 and capacitor C6 which is coupled to the output circuit through coil L3 and connected to the control grid of tube Vi is adjusted to provide a relatively broad resonance at the selected mechanical harmonic of the transducer. Such adjustment results in maximum current feedback at this one harmonic, and oscillator operation is sustained at this point.

' Although this invention has been described with a certain degree of particularity, it is to be understood that the present disclosure has been made only by way of example,

8 tion means between the said Wall and housing so arranged, as to provide partitioned first and second heat exchange compartments, said combustion chamber having first and second zones adapted to operate at different temperature ranges, said first heat exchange compartment being adapted to contain a heat exchange fluid and being located adjacent said first zone, a first series of thermoelectric'couple means operable to produce maximum electrical output Y within a first temperature range having hot junctions within said rst Zone and cold junctions in said first heat eX- change compartment, said second heat exchange compartment being adapted to contain a heat exchange fluid and being located'adjacent said second zone, a second series of thermoelectric couple means operable to produce maximum electrical output in a second and different temperature range having hot junctions Within said second zone and cold junctions in said second heat transfer compartment, and connecting means for combining the power outputs of both said series to supply operating power to UNITED STATES PATENTS 1,599,323 9/26` Frank. 2,015,610 9/35 Findley. 2,3 62,25 8 11/44 Findley 126--110 v2,362,259 11/44 Fndley 126-110 X 2,453,595 11/48 Rosenthal. 2,481,620 9/ 49 Rosenthal Y 158-77 `2,519,241 8/50 Findley a 126-110 X 2,949,900 8/ 60 Bodine. v3,121,534 2/64 Wilson 239--102 JAMES W. WESTHAVER, Primary Examiner.

FREDERICK L. MATTESON, JR., ROBERT A.V

OLEARY, Examiners.

Claims (1)

1. IN APPARATUS OF THE CHARACTER DESCRIBED, THE COMBINATION WHICH COMPRISES A POWER OPERATED LIQUID FUEL BURNER, HOUSING MEANS ADJACENT SAID BURNER AND ENCLOSING A WALL WHICH DEFINES A COMBUSTION CHAMBER FOR SAID BURNER, SAID WALL BEING SPACED FROM SAID HOUSING, PARTITION MEANS BETWEEN THE SAID WALL AND HOUSING SO ARRANGED AS TO PROVIDE PARTITIONED FIRST AND SECOND HEAT EXCHANGE COMPARTMENTS, SAID COMBUSTION CHAMBER HAVING FIRST AND SECOND ZONES ADAPTED TO OPERATE AT DIFFERENT TEMPERATURE RANGES, SAID FIRST HEAT EXCHANGE COMPARTMENT BEING ADAPTED TO CONTAIN A HEAT EXCHANGE FLUID AND BEING LOCATED ADJACENT SAID FIRST ZONE, A FIRST SERIES OF THERMOELECTRIC COUPLE MEANS OPERABLE TO PRODUCE MAXIMUM ELECTRICAL OUTPUT WITHIN A FIRST TEMPERATURE RANGE HAVING HOT JUNCTIONS WITHIN SAID FIRST ONE AND COLD JUNCTIONS IN SAID FIRST HEAT EXCHANGE COMPARTMENT, SAID SECOND HEAT EXCHANGE COMPARTMENT BEING ADAPTED TO CONTAIN A HEAT EXCHANGE FLUID AND BEING LOCATED ADJACENT SAID SECOND ZONE, A SECOND SERIES OF THERMOELECTRIC COUPLE MEANS OPERABLE TO PRODUCE MAXIMUM ELECTRICAL OUTPUT IN A SECOND AND DIFFERENT TEMPERATURE RANGE HAVING HOT JUNCTIONS WITHIN SAID SECOND ZONE AND COLD JUNCTIONS IN SAID SECOND HEAT TRANSFER COMPARTMENT, AND CONNECTING MEANS FOR COMBINING THE POWER OUTPUTS OF BOTH SAID SERIES TO SUPPLY OPERATING POWER TO THE BURNER.

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